The present invention relates generally to a hermetic compressor and, more particularly, to such a compressor including a compressor mechanism within a housing, wherein the mechanism is operably driven by a rotatable crankshaft having an axial shaft portion and a radially extending plate portion. The plate portion typically functions as a counterweight and/or a crankshaft thrust collar.
More specifically, the present invention relates to a hermetic compressor including within a housing a compressor mechanism, i.e., a scroll compressor mechanism, wherein the crankshaft experiences axial loading due to various forces acting thereon, including the weight of the crankshaft. Axial loading of the crankshaft can cause damage to crankshaft supporting thrust surfaces or, alternatively, require expensive thrust bearings to avoid such damage. In the case of a crankshaft exposed entirely to atmosphere, crankshaft balancing is not necessary. However, in hermetic compressors wherein the crankshaft is subjected to internal pressures of the compressor, the crankshaft is typically balanced by exposing equal and opposite areas of the crankshaft to equal pressures.
The aforementioned axial loading and corrective balancing of a crankshaft presents special problems in the case of a hermetic scroll-type compressor. A typical scroll compressor comprises two facing scroll members, each having an involute wrap, wherein the respective wraps interfit to define a plurality of closed pockets. When one of the scroll members, i.e., the orbiting scroll member, orbits relative to the other, the pockets travel to compress and convey refrigerant fluid from a suction pressure chamber to a discharge pressure chamber. During operation of a scroll-type compressor, the pressure of compressed refrigerant at the interface between the scroll members tends to force the scroll members axially apart. Consequently, axial compliance of the orbiting scroll member toward the fixed scroll member is required. In many instances, this involves exposing the bottom side of the orbiting scroll member to fluids at the various pressure levels existing within the housing. This can cause additional axial loading on the crankshaft if care is not taken to assure crankshaft balancing.
One axial compliance mechanism used in scroll compressors for applying an axial compliance force to the orbiting scroll member involves providing an intermediate pressure chamber defined by the bottom of the orbiting scroll member and a frame member. In such a system, the crankshaft plate portion may be entirely enclosed within the intermediate chamber, thereby exposing the top and bottom surfaces of the plate portion to substantially the same pressure, i.e., zero net axial force. However, other axial compliance mechanisms exist that expose the top and bottom surfaces of the plate portion to separate pockets of fluid. In such a system, even though the separate pockets may be supplied fluid from a common source, fluid feed and outlet paths associated with the individual pockets may result in slightly different pressures, i.e., a net axial force on the plate portion. The aforementioned pressure differences are unpredictable and, therefore, make crankshaft balancing more difficult.
A further problem associated with crankshafts having a radially extending plate portion is that flow of lubricating oil along the axial length of shaft portion of the crankshaft, either for delivery or venting, may be interrupted by the plate portion. Such a condition in scroll compressors can lead to introduction of excessive oil into the refrigeration system, thereby causing system inefficiencies.
The present invention is directed to overcoming the aforementioned problems associated with a compressor oil delivery system, wherein it is desired to provide improved axial balancing of a crankshaft having a radially extending plate portion.